The document outlines the fundamentals of memory interfacing, including data storage, address generation, and memory organization. It discusses the importance of address and data connections, control inputs, and the significance of timing diagrams in communication protocols. Practical applications are noted, along with a brief assignment to explore various types of memory systems in industry.

1. Memory Interfacing

2. Memory Basics
• Memory is generally divided into locations that store a fixed amount
of data. (usually a byte)
• For the entire memory to be useable, the processor should be
capable of generating a unique address for each location.

3. • The total number of unique addresses that can be generated by the
processor is referred to as its address space.
• The size of the address space is limited by the width of the address
bus by:
Where n is the width of the address space.
• What do we really mean when we refer to a memory size of 1GB?

4. Memory connections

5. Address Connections
• All memory devices have address inputs that select a memory
location within the memory device.
• They are usually labelled from the least significant address input to ,
the most significant.
• A 1K device has 10 address pins; labelled .
• Memory addresses are usually represented in hexadecimal.
• Example: 400H represents 1K-bytes. If a memory device is decoded to
begin at address 1000H, and it is a 1K device, what is the address of
the last memory location?
• Others you should keep in mind: 1000H : 4K, 10000H : 64K, etc

6. Practical Application
Processors have a limit on how
much memory they can make
use of based on the address
space.

7. Memory can be organized in different ways:
8 x 1 byte
or
8 x 8 bit
16 x 4 bit
64 x 1 bit
capacity of all these is 64 bits

8. Data Connections
• All memory devices have a set of data outputs or input/outputs. The
figure in slide 4 has a set of common I/O pins.
• The data connections are the points at which data is entered for
writing or extracted for reading.
• Data pins on memory devices are almost always labelled Do – D7 for an
8-bit wide memory device. (Often called byte-wide memory)
• It is however possible to have 16-bits, 4-bits, or just 1-bit wide
memory devices.

9. • Catalogue listings of memory devices often refer to memory locations
times bits per location.
• Example: 1K x 8, 16k x 1, etc.
• Memory devices are also classified according to the total bit capacity.
• Example: 1K x 8 may be listed as 8K, 64K x 4 as 256K, etc
• Variations occur across manufacturers.

10. TEST YOUR UNDERSTANDING!
• Why is the data bus bi-directional?
• If a 32 bit microprocessor system is designed to access a memory
system of total of 256 K bytes what is the data bus and the address
bus lengths of the system.

11. Selection Connections
• Each memory device has an input that selects or enables the device.
• (Refer again to image on Slide 4)
• This input is often called a chip select (CS or ) or chip enable (CE or ).
It is sometimes simply referred to as a Select (S or ) input.
• If this input is active the memory device performs a read or write. If it
is inactive, the memory device is disabled.

12. Control Connections
• All memory devices have some form of control input(s).
• This input determines what kind of action is performed on the device.
• A ROM usually has one control input, the output connection ( or gate
( input. (Why?)
• A RAM device has one or two control inputs.
• If there exists only one control input it is usually labelled .
• If there are two control inputs, they are labelled and

13. Read and Write Protocols
Timing Diagrams
• Most common method for describing a communication protocol is by
the use of timing diagrams.
• On a timing diagram, time proceeds to the right on x-axis.
• A control signal is shown with a single line and may by low or high at
some intervals.
• A signal may be active low (e.g., G’, , or G_L).
• The term assert is used to indicate that the signal is made active and
deassert means deactivated. Asserting G means set G=0.

14. • Deassert for an active low signal:
• Data signals on the other hand are usually represented by a single line
when inactive and a ‘double’ line when active.

15. Read Protocol

16. Write Protocol

17. TEST YOUR UNDERSTANDING…
•Can you explain the difference between these
three terms:
•Setup time, read time, write time?

18. Assignment.
 Read about different types of memory systems in use in today’s
industry.
 ROM, RAM, Disk, Cache, etc.